Dilute, aqueous solutions of lower organic peracids, especially of peracetic acid, are effective against a wide spectrum of microorganisms, including algae, fungi, bacteria, and viruses. Because they leave only the corresponding lower organic acids as residues, they are particularly suited for applications in which a non-environmentally-polluting disinfectant is required.
Dilution of concentrated solutions of organic peracids to form dilute peracid solutions is undesirable. Concentrated solutions of organic peracids not only present a risk of fire and rapid decomposition with the liberation of gases but also are a potential risk to the user due to attack on the skin and nasal mucous membranes by the peracid. Dilution also causes a disequilibrium that, over time, reduces peracid concentration and the antimicrobicidal efficiency.
An organic peracid can be formed from the corresponding acid and hydrogen peroxide by the following equilibrium reaction: EQU R--CO--OH+H.sub.2 O.sub.2 .revreaction.R--CO--OOH+H.sub.2 O(I)
where R is an organic radical, typically a lower organic radical of 1 to 5 carbon atoms.
In dilute solutions a relatively long period of time is required to attain equilibrium because of the low concentration of the reactants. The increase in peracid concentration slows considerably as the equilibrium concentration is approached, even when concentrated solutions are used. Although an equilibrium solution containing 35% by weight peracetic acid can be prepared in about one to two days, preparation of an about 5% by weight solution of peracetic acid requires about 11 to 14 days, even in the presence of acid catalysts. Consequently, preparation of a dilute, aqueous solution of lower organic peracids by the equilibrium method is time consuming, resulting in inefficient use of plant and equipment.
Various attempts to prepare peracids have been disclosed. Greenspan, U.S. Pat. No. 2,90,800, prepared concentrated peracetic acid by reaction of concentrated hydrogen peroxide with glacial acetic acid in the presence of an acid catalyst, followed by addition of acetic anhydride to remove water.
Oringer, U.S. Pat. No. 3,432,546, discloses a process for the production of an aqueous peracetic acid solution by the reaction of hydrogen peroxide with acetic anhydride in a tubular reaction zone. However, a non-equilibrium mixture of acid, peracetic acid, hydrogen peroxide, and water, which is not suitable for storage and shipment, was produced.
Crommelynck, U.S. Pat. No. 4,297,298, discloses a process for formation of dilute solutions of organic peracids in which a concentrated solution of peracid is diluted with water and permitted to hydrolyze in the presence of an acid catalyst and then diluted with at least one of the reagents used to prepare the concentrated solution. However, this process can require up to 48 hours to attain equilibrium.
Brougham, U.S. Pat. No. 5,349,083, discloses a process in which a dilute solution having an equilibrium composition is produced by contacting concentrated hydrogen peroxide with a concentrated lower aliphatic acid to rapidly form an aqueous reaction mixture rich in peracid and diluting the reaction mixture with water and the quantities of acid and hydrogen peroxide required to reproduce the equilibrium composition of the dilute solution. Dilution is carried out before the reaction mixture has reached equilibrium. Although this process reduces the time to produce the dilute peracid solution, several hours is still required to produce a solution that contains about 21-25% by weight peracetic acid, the preferred concentration for dilution.
Thus, a need exists for a faster process for producing dilute, aqueous solutions of lower organic peracids suitable for storage and shipment.